Method of molding



3m 1947. J. P. GITS METHOD OF MOLDING Filed Dec. 14, 1940 Patented Jan.7, 1947 METHOD OF MOLDING Jules P. Gits, Chicago, Ill., assignor, bymesne assignments, to himself and Joseph A. Gits,

Chicago, Ill.

Application December 14, 1940, Serial No. 370,111

7 Claims.

Ihis invention relates to articles produced from thermoplastic materialand is more specifically directed to an improved method and means forcontrolling the tenacity of certain types of thermoplastic articles atlow temperatures without experiencing uneven shrinkage in the moldingoperation whereby breaks and fractures resulting from brittleness at lowtemperatures are effectively prevented.

It seems that brittleness of thermoplastic materials at low temperaturesis an undesirable characteristic that has caused much trouble. Insertshave been heretofore used by have proven generally unsatisfactorybecause they cause uneven shrinkage during the molding operation andleave shrinkage marks on the exterior surface that are very undesirable.Experience has shown that this brittleness will occur at temperatures inthe neighborhood of a few degrees above zero degree Fahrenheit and thatwhen thermoplastic articles are subjected to this temperature, they willreadily break or fracture if roughly handled. Experience has furthershown that many articles produced from thermoplastic material arefrequently exposed to these low temperatures during normal use. It hasbeen recently discovered that flashlight barrels made of thermoplasticmaterial would readily fracture and break under cold weather conditionsand that the fracture or break would usually occur each time at the samelocation. The normal use of such devices in Winter obviously brings theminto contact with low outside temperatures and their utility asflashlight devices will only be as valuable as their ability towithstand the low temperatures. On the other hand, panel and instrumentboards produced from thermoplastic material and used on motor vehicleswere likewise recently discovered to fracture and break, although notsubjected to blows or other strains that normally tend to damage thistype ofmaterial. It was found that the vehicles had been exposed to lowoutside temperatures, and, under such conditions, mere road vibrationwas sufficient to fracture and break these thermoplastic panels.

Broadly, the invention is directed to a novel type of means and methodof employing said means in the injection molding of thermoplasticmaterials whereby the tenacity of articles produced from these materialsmay be controlled to prevent breakage and fracturing resulting frombrittleness at low temperatures and whereby the incorporation of saidmeans by said method disclosed herein will effectively eliminate uneven2 shrinkage of the materials during the molding operation.

One object of the invention resides, therefore, in the provision of anovel method of incorporating the aforesaid means in the form of alining or other equivalent means so as not to interfere with uniformshrinkage of the thermoplastic material while hardening whereby thismaterial, when thus formed, will resist any tendency to break orfracture at low temperatures and articles of uniform quality andappearance may be produced therefrom.

A further object of the invention resides in the novel type of meansincorporated in the molding of thermoplastic materials whereby thecontraction of these materials upon hardening may be uniform and unevenshrinkage will be prevented. It is found that one form of suitable meansmay be a fibrous lining, fabricated in any desirable way as by weaving,felting or pressing, that al lows the thermoplastic materials tocontract uniformly, this form of lining preferably being devoid of anappreciable expansion and contraction upon heating and cooling, or of adegree of expansion and contraction that will interfere with the'expansion and contraction of these thermoplastic materials so as not toresult in uneven contraction during the molding operation.

A still further object of the invention is to provide a fibrous liningthat may form, if so desired, but a small part of the wall thickness andmay be inserted along the inner surface during the molding operation. Incertain instances, it is sufficient to affix this lining to coverlimited areas that are subjected to greater strain and therefore moreapt to break or fracture at low temperatures than other portions of thedevice. By making this lining of a fibrous character, the fibers thereinare believed to yield with respect to each other and the thermoplasticmaterial as it contracts so as not to retard shrinkage of the material.Consequently, shrinkage marks will not appear. I believe that thelining, although thin and fibrous in character and therefore practicallydevoid of structural strength, tends to distribute the strain imposedupon the thermoplastic material so that a sudden blow will not locallyfracture the material.

I do not wish to confuse the means and method disclosed herein with theuse of fibrous filling ma terials, such as cotton flock, comminutedpaper or pulp, shredded cloth, wood shavings and sawdust, which not onlyfail in their purpose materially to strengthen resinous materialsagainst breaks or fractures resulting from brittleness produced by lowtemperatures but ver materially interfere with the molding operationsand character of the finished product. Usually, these fibrous fillersare coarse and too long to feed through extremely small passage betweenthe sprue and mold cavity. To overcome this difficulty, the fibrousfilling has been directly introduced into the mold cavity before it isclosed prior to the introduction of the plastic material therein, butsuch procedure is not satisfactory because it materially interferes withrapidity of operation, increases costs and does not'assure a uniformmixture of the fibrous filling with the plastic material. Although auniform mechanical mixture of synthetic resin and a finely comminutedfiller might be introduced through the gate passages under relativelyhigh pressures, the final product would invariably show traces ofuncovered filler as a result of the first portions of the compositionforced through the gate passages under these high pressures not havingsufficient resistance to flow to permit proper impregnation during themold cavity filling cycle. It will be noted that there are manyobjections to introducing the filler into the plastic material duringthe molding operation. The finished product will have a greater densityand in certain respects greater strength but the material between theinterspersed filler will still be brittle at low temperatures and liablein the same degree as before to breakage and fracturing.

My improved fibrous lining advantageously allows a distribution of anystrain that may be produced from a blow and the entire wall structurecan thereby be protected which would not be obtained if fibrous fillingis first mixed with the plastic material during the molding operation.Aside from this obvious advantage, I find that the use of my improvedmeans further admits of simpler and cheaper molding operations whichobviate troublesome steps during the transfer or injection of theplastic material into the mold cavity that obviously cause delay andincrease production costs.

When the fibers of the fabric lining or insert are not impregnated bythe thermoplastic material, they are free to yield with respect to eachother and to the thermoplastic material so as not to retard shrinkage ofthe material and peculiarly to advantageously distribute any strainimposed upon the thermoplastic material by a sudden blow.

Also, my invention is concerned with the aforesaid insert or lining of aform-retaining character and particularly applicable to injection typeof molding for producing cylindrical shell structures, such asflashlight barrels, formed upon mandrels in mold cavities having theheated fluid plastic material injected thereinto under relatively highpressures.

The lining or insert may be of a fabric material that readily retainsits form, or of a character that first requires a preforming treatmentto give it the rigidity necessary to be form-retaining, which mayinclude a built-up structure of laminated fiber and plastic material, orfiber coated with any suitable substance which may be a plastic materialsuch as cellulose acetate.

By making the lining or insert form-retaining, it will be impossible forthe plastic material being injected to find its way under the lining or.insert and thereby be raised from the mandrel or die surface againstwhich it is positioned in the mold and forced outwardly so as to beexposed 4 to the outer surface of the thermoplastic wall of the finishedarticle.

As a part of the improved process herein disclosed, it is contemplatedthat the injection of the fluid plastic material will be made undertemperature conditions keeping the temperature of the lining or insertlower than that of the injected material so that, although there is anapparent permanent bond between the lining or insert and the injectedmaterial by virtue of the pressures used, the injected material will notimpregnate the lining or insert and obstruct the relative freedom ofmovement of the fibers of the lining or insert.

Other objects and advantages of the invention will be apparent from thefollowing detail description when taken in connection with theaccompanying drawing.

In the drawing:

Figure 1 is an elevational view of a flashlight barrel to which thepresent invention is adapted for the purpose of illustrating one form ofembodiment thereof;

Fig. 2 is a vertical sectional View of a flashlight barrel with its endpieces and manually operable member removed;

Fig. 3 is a perspective View of a portion of the wall of the flashlightbarrel to illustrate the application of the present invention to acylindrical wall;

Fig. 4 illustrates on of the first steps in the novel method hereindisclosed which involves placing the insert upon the core or mandrel andlocating the same at the proper position by a tapered relation betweenthe insert and the core, or by a shoulder on the core;

Fig. 5 illustrates a mold having a cavity for receiving the mandrel;

Fig. 6 is a sectional view illustrating the relative thickness that thelining or insert may have with respect to the body;

Fig. '7 illustrates head gear in the form of a helmet made of plasticmaterial and embodying the present invention; and

Fig. 8 illustrates the manner of placing a formretaining insert upon thesurface of a mold cavity so that it will maintain its proper positionduring the injection of the plastic material into the mold cavity.

For the purposes of illustration, the invention is shown first inconjunction with the molding of a cylindrical shell used, for example,as a flashlight barrel, and then in conjunction with any cylindricalmember. It will be apparent, 55 therefore, that the principle embodiedmay be applied to the formation of many articles and that from itsbroadest aspects the invention is not to be limited to any givenapplication, al-

though it has a unique and'practical use as a 0 backing adapted to beapplied to areas that tend more readily to fracture and break.

Fig. 1 illustrates a complete shell or barrel I of a flashlight having afront end 2 carrying the usual lens and light bulb (not shown) and arear tip 3 fitted as by threading so as to close off the rear end as isusually customary in this type of article. The barrel is preferablycylindrical and carries a number of batteries (not shown). It isprovided with longitudinal ribs 4 and a series of raised portions 5 onopposite sides of an opening 6 through which a manually operable memberi connects to the usual circuit making and breaking member (not shown).

Shell or barrel 1 is molded of plastic material by means of a suitabledie which, for purposes of illustration, comprises a head plate 8carrying a core 9 which extends into a mold cavity It formed by twowedge-shaped die members I I and l2, slidably movable along side members43 and hi anchored to said head plate 8. Knockout pins l are adapted tolie in openings It provided in head plate 8 so that, through a knockoutplate l'l carried at their outer ends, heads IS on their inner ends maybe forced inwardly to engage and move die members I! and 2 whereby tospread the same outwardly and away from each other along the taperedsides of members It and M.

A front plate'lS- is adapted to carry sprue l9 and the usual gate whichcommunicateswith mold cavity Hi. When a charge of plastic material .isintroduced through sprue It and gate 20 into mold cavity l0, plate [8 istightly held in its position, as shown in Fig. 5, so'that mold cavity I0is closed. Pressure may be maintained upon this plastic material as itis introduced until mold cavity In is filled. This pressure can be momentarily held upon the material to assure that the material completelyfills the mold cavity. Lie members H and I2 may be heated or cooled byhotor cold fluid flowing through passages 2!, while head member l8 maybe provided with passages 22 for similar purposes. If thermosettingresinous materialsare used, the temperature of head member l8 will bemaintained at a point sufiicient to hold the materials in a plasticcondition while the temperature of die members l3 and M will be at ahigher point to effect a reaction and set the materials in the moldcavity. Transfer molding of thermosetting materials merely requires thematerials to be held at the temperature keeping the materials in aplastic state in the primary or pressure chamber so that they may bereadily passed into the mold cavity heated at a higher temperature toeffect a reaction. If thermoplastic materials are used, the temperatureof head member l8 will be high enough to hold the materials in a plasticor free flowing condition while the temperature of die members l3 and Mwill be similarly maintained until the mold cavity is filled whereuponthe die members may be chilled momentarily to set the materials. It willbe quite apparent, therefore, that the process herein disclosed is notlimited to the type of material used. The type of material to be usedwill depend upon application of the invention to control the tenacity ofa given product so that it will not readily fracture or break.

I havefound, for example, that in flashlight barrels or shells there isa tendency for a certain area thereof to break or fracture before theremaining portion yields, and this area is shown generally as A in Fig.2 for the construction of flashlight barrel illustrated. It seems thatcertain plastic materials become exceedingly brittle at low temperaturesand fracture or break at this area A if subjected to strain by forcesoccurring through normal handling. It will be understood that thetensile strength does not necessarily become impaired but that amolecular reaction occurs that causes a brittleness which is veryundesirable from a practical standpoint of use.

I find that the undesirable fracturing or breaking caused by thisbrittleness at low temperatures can be effectively overcome by a simpleand inexpensive means in the form of a layer or sheet of shock absorbingmaterial, preferably of a fibrous character, and may be cardboard, orthe like, that is form-retaining when placed in the mold' and subjectedto the pressure of the plastic material being injected. This material isshown sleeve and placed upon core 9 before the'mold is closed. I findthat core B'may be slightly tapered, or, if desired, provided with ashoulder: 21 to facilitate locating material 25 upon core 9 at area A.This material 25 may be any fibrous material, like that of cardboard,which can be fabricated to be form-retaining. It may be fabric materialpressed into form like cardboard or it may be fabric material that iswoven or felted and then pressed into form with a relatively compactformation of the fibers to prevent penetration of the plastic material.It is also found that penetration of the fibers can be prevented if asmooth outer surface is provided. When material 25 is notform-retaining, the pressure of the in jected plastic material willcause the material either to wrinkle or roll back upon itself along thecore,'or the plastic material will force its way under the material andraise the same away from the core, so that this material will lie in thearea of the wall and be irregularly exposed along the outer surface. Incertain instances, looselyfabricated material or other non-formretaining material can be used by subjecting it to a preforming step bycoating it with a layer of plastic material before placing it upon core9. In this connection, the invention extends to any lining or insert ofthe kind described that can be made form-- retaining for the purposesdescribed and have a sufficient portion of its individual fibersyieldable with respect to each other and to the plastic material as itcontracts and at the same time serve as a cushion to absorb a blow so asto distribute the strain imposed along the wall. Such other materialsthat may be used are felt, heavy paper, canvas, etc., that are in acondition of being formretaining, or pre-treated to be form-retaining,with a relatively smooth outer surface, so that the fibrous materialwill be compressedly embedded in the plastic material withoutimpregnation of the fibers restricting their freedom of movement whenreleased from pressure and so that the fibers are free to yield to thecontracting action of the plastic material.

As previously stated, the plastic material may be injected underpressure until mold cavity Ill is filled and the plastic material isforced to surround material 25 on all sides except the surface againstcore 9. This pressure is held momentarily until material 25 is firmlyembedded on three sides whereupon it is released. The plastic materialis then allowed to set, either by cooling if thermoplastic or by heatingit thermosetting. When the mold parts are opened and the molded productis removed from the mold cavity, material 25 will .be found to be a partof the molded product and firmly held thereby. The exposed surfacecontacting the surface of the mold cavity,which would be the surfacecontacting core 9, as shown in Fig. 5, will be smooth and flush with theinner surface of the molded product. It will be formed as part of thewall and tightly afiixed thereto in recessed relation. Whetherthermosetting material or thermoplastic ma terial is used as the plasticmaterial injected into the mold cavity to form the molded productdesired, core 9 is preferably held at a temperature lower than. thetemperature of the injected plas Although the plastic material may beinjected into mold cavity Ill under pressure, material will be firmlyembedded without impregnation of its fibers to the extent of restrictingtheir freedom of movement when the pressure is released. It is quitedesirable that material 25 be of a char.- acter devoid of appreciableexpansion and contraction upon heating and cooling, or at least of adegree of expansion and contraction that will not interfere with theexpansion and con-- traction of the plastic material so as notto resultin uneven contraction'of the plastic material when it sets. Material 25is in a layer that is appreciably thin with respect to the thickness ofthe wall carrying the same in the finished product. Its fibers may becompactly held together. It will not interfere with the contraction ofthe plastic material when the latter sets because the fibers thereofarefree to move. Consequently, shrinkage of the plastic material will beuniform. Shrinkage marks heretofore resulting wherever inserts have beenissued are eliminated.

Due to the character of material 25, any blow or exterior force broughtto bear against area A of the finished product will not result in astrain fracturing or breaking the wall. The strain will be uniformlydistributed by material 25. In other words, material 25 advantageouslyserves as a cushion to absorb the blow and thereby protect the wall fromfracturing or breaking.

It is not intended that material 25 should be formed only as a sleeve asshown in Figs. 2, 4 and 5. Material '25 may be formed in pieces of anyshape to conform to the contour of the inner wall surface of thefinished product and of any size to protect a given area of the finishedproduct. In Fig. 3, material 25 is shown as a backing. for a limitedarea of an arcuate wall 26. 'Fig. 6 illustrates the approximatethickness of material 25 with respect to the finished wall. Thisthickness may vary, but I find that it may be small and very effectivelyaccomplish the desired results.

In Figs. '7 and 8, another type of device is shown to illustrate howmaterial 25 may be aptly used as a lining or insert and by reason of itsformretaining condition be held upon a cavity surface Without beingdisplaced by the pressure of the injected material. For the purposes ofil1us-' tration, this device may be a helmet of plastic material withmaterial 25 disposed about'its inner surface. Material 25 maybe of ashape conforming to this inner surface so that it will rest firmlyagainst the cavity surface of diemember 36, as illustrated in Fig. 8.Outer die member 31 cooperating with die member 36 forms the cavity 38in which helmet 35 will be formed when the plastic material is injectedthrough spru'e passage 39.

The present invention is designed to provide a simple, practical,inexpensive and very effective form of protective lining or insert ofthe type described that 'is'particularly applicable to a cylindricalwall in the form of a flashlight bar-' rel made of plastic materialwhich normally becomes brittle under low temperatures and readilyfractures and breaks, as well as a novel method of incorporating thislining or insert in a Wall of this type during the molding operation.Not only the wall reinforced against fracturing and breaking andshrinkage marks upon the exterior surface thereof prevented, but aconsiderable saving in the use of the plastic material results becausethe lining or insert may be a material that is less expensive than theplastic material and the labor used in applying it to the core beforeeach operation, due to its form-retaining condition, is negligible.

This application is a continuation in part of copending application,Serial No. 326,372, filed March 28, 1940.

Without further elaboration, the foregoing will so fully explain thegist of my invention that others may, by applying current knowledge,readily adapt the same for use under varying conditions of service,without eliminating certain features, which may properly be said toconstitute the essential items of novelty involved, which items areintended to be defined and secured to me by the following claims.

I claim:

1. The method of forming a relatively thin tubular shell of plasticmaterial such as a flashlight barrel with a medium disposed along itsinner surface to act as a, shock absorbing device pre venting fracturingor breaking of the plastic material but without causing shrinkage marksto form upon the outer surface of the plastic material which comprisesforming a fabric material into a form-retaining tube with its fiberscompactly compressed but yieldable with respect to each other and with arelatively smooth outer surface, placing said tube upon a die corehaving an external diameter substantially equal to the internal diameterof said tube, rendering workable and fluid by heat a mass of plasticmaterial and injecting the fiuid mass into the die of said core to flowabout said tube and fill the cavity of said die containing said core,and employing a pressure to inject the fluid mass that will compressedlyembed said tube in said plastic material without impregnating the fibersof sai tube along its said smooth outer surface and without restrictingthe relative yieldability of the individual fibers of said tube or theiryield-.

ability with respect to contraction and expansion of said plasticmaterial.

2. The method of forming a tubular shell such as a flashlight barrelwhich comprises providing a thin tubular layer of fabric material informretaining condition, the fabric layer having an external diameterless than the external diameter of the member to be formed but aninternal diameter that is substantially the same as the internaldiameter of said member, rendering workable and fluid by heat a mass ofplastic material, placing the fabric layer in a die provided with a coreof substantially the same external diameter as the internal diameter ofthe fabric layer, and forcing the heated fluid mass of plastic materialthrough out end of the die to fill the space in the die about the coreand the fabric layer.

3. The method of forming a tubular shell such as a flashlight barrelwhich comprises forming fabric material into a, form-retaining tube withits fibers compactly compressed but yieldablewith respect to each otherand with a relatively smooth outer surface, placing said tube upon a diecore having an external diameter substan tially equal to the internaldiameter of said tube, 3 rendering workable and fluid by heat a mass ofplastic material and injecting the fluid mass into the die of said coreunder a pressure causing the fluid mass to flow about the tube and fillthe cavity of said die, and employing a pressure to inject the fluidmass compressedly to embed the tube in the plastic material withoutimpregnating the fibers or restricting the fibers to yield to thecontracting action of the platsic material.

4. The method of forming a relatively thin tubular shell of plasticmaterial such as a flashlight barrel with a medium disposed along and toform a portion of its inner surface to act as a shock absorbing devicepreventing fracturing or breaking of the plastic shall but withoutcausing shrinkage marks to form upon its outer surface of the plasticshell which comprises forming a fabric material into a form-retainingbody, placing said fabric form-retaining body upon a die core having anexternal diameter substantially equal to the internl diameter of saidplastic shell to be formed, the form-retaining condition of said bodyholding the same against said core in a relatively rigid formation,injecting a fluid mass of plastic material into the die of said coreuntil the die cavity is filled, and employing a pressure to inject thefluid mass of plastic material that will compressedly embed said fabricbody therein without restricting the freedom of the fibers thereof toyield to contraction and expansion of the plastic material.

5. The method of forming a relatively thin tubular shell 'of plasticmaterial such as a flashlight barrel with a medium disposed along and toform a portion of its inner surface to act as a shock absorbing devicepreventing fracturing or breaking of the plastic shell but withoutcausing shrinkage marks to form upon its outer surface of the plasticshell which comprises form-v ing a fabric material with a form-retainingbody, placing said fabric form-retaining body upon a die core having anexternal diameter substantially equal to the internal diameter of saidplastic shell to be formed, the form-retaining condition of said bodyholding the same against said core in a relatively rigid formation,injecting a fluid mass of plastic material into the die of said coreuntil the die cavity is filled, the temperature of said fabric bodybeing below the temperature of the fluid mass of plastic material as itenters the die cavity and contacts said fabric bo y, and employing apressure to inject the fluid mass of plastic material that willcompressedly embed said fabric body therein but without impregnation ofthe fibers of said fabric body restricting the freedom of the fibers toyield to contraction and expansion of the plastic material.

6. A method of forming a relatively thin tubular shell of plasticmaterial such as a flashlight barrel which comprises compactlycompressing a fibrous material into a forming-retaining tube with arelatively smooth outer surface, rendering workable and fluid by heat amass of plastic material, placing said form-retaining tube upon a coreof a die and injecting the fluid mass into the cavity of said die tocause the fluid mass to flow about the core and the form-retaining tubewithout displacing the latter from its position upon the core, andemploying a pressure to inject the fluid mass to compressedly embed saidform-retaining tube in the fluid mass without impregnating the fibersthereof or restricting the relative yieldability of the fibers withrespect to contraction and expansion of the plastic material.

7. A method of forming a relatively thin tubular shell of plasticmaterial such as a flashlight barrel which comprises providing a fibrousmaterial into a form-retaining body capable of holding itself againstthe surface of a core extending into a die cavity, rendering workableand fluid by heat a mass of plastic material, placing saidform-retianing body against the surface of a core, injecting the fluidmass of plastic material into the die cavity, and employing a pressureto inject the fluid mass that will compressedly embed said fibrousmaterial therein along its inner surface without impregnating the fibersthereof.

JULES P. GITS.

